With the advantageous fluxes of reactive species such as ions and radicals, plasma-based surface treatment methods have been extensively used. In the conventional plasma-based surface treatment methods, the plasma is generated in a high temperature and high pressure chamber. As such, it is limited to select the conventional plasma processing technique for treating the material having a low melting point such as plastic. Additionally, the conventional plasma processing requires high capital cost for maintaining a vacuum chamber and the space limit of the vacuum chamber is infeasible for treating large workpiece.
In order to solve these problems, an atmospheric plasma processing technique, which is feasible in an atmospheric pressure and temperature, has been proposed. Here, the atmospheric pressure means the pressure exerted by the atmosphere as a result of gravitational attraction. Using the atmospheric plasma (or low temperature plasma), it is possible to perform the surface treatment on the material having a low melting point such as plastic without damaging the surface of the material or changing physical properties of the material. The atmospheric plasma processing technique allows iterative surface treatments, thereby dramatically increasing the productivity. Also, processing materials at atmospheric pressure reduce the capital cost of the vacuum chamber and eliminates restriction to the size of the workpiece.
FIG. 1 is a cross sectional view illustrating a conventional atmospheric plasma generation apparatus disclosed in Korean Patent Laid-Open Publication No. 10-516329 filed by the same applicant.
In FIG. 1, the plasma generation apparatus 100 includes a power supply electrode 110, a main plasma ground electrode 120, an auxiliary plasma ground electrode 130, a gas flow passage 140, and a power source 150.
The power supply electrode has a long cylindrical shape. The main plasma ground electrode 120 is arranged below the power supply electrode 110, and the auxiliary plasma ground electrode 130 is arranged at one side of the power supply electrode 110. The power supply electrode 110 is coated by a dielectric layer 111. The gas flow passage 140 is formed between the power supply electrode 110 and the auxiliary plasma ground electrode 130 for supplying gas.
The power source 150 supplies radio frequency (RF) power to the power supply electrode 110. In order to match the RF power to the power supply electrode 110, the plasma generation apparatus 100 further includes a matching box (MB) 150.
The gas flow passage 140 is provided with a first passage 141, a second passage 143, a plurality of orifices 145, and a gas mixture chamber 147. The first passage 141 receives the gas input from outside of the plasma generation apparatus 100, and the second passage 143 is connected to the first passage 141 and formed in parallel with the power supply electrode 110. The orifices 145 are formed along the longitudinal direction of the power supply electrode 110 so as to be connected to the second passage 143. The gas mixture chamber 147 is formed along the longitudinal direction of the power supply electrode 110 and connected to the orifices 145 independently. The gas mixture chamber 147 is connected to a discharge space formed between the power supply electrode 110 and the auxiliary plasma ground electrode 130. A workpiece (M) is transferred to be positioned between the power supply electrode 110 and the main plasma ground electrode 140.
The plasma generation apparatus 100 of FIG. 1 can generates auxiliary plasma at a low voltage since the auxiliary plasma ground electrode 130 is positioned close the power supply electrode 110. As passing the auxiliary plasma, the energy level of the gas increases such that the gas passing the reactive space between the power supply electrode 110 and the main plasma ground electrode 120 can be changed to the plasma state with low voltage.
In the conventional plasma generation apparatus 100 of FIG. 1, however, the cylindrical power supply electrode is connected to the power source 150 at its one end such that the RF power is not uniformly applied to the power supply electrode 100 in its longitudinal direction, resulting in unstable generation of plasma.
Also, the convention plasma generation apparatus 100 is configured such that the outlets of the orifices 145 are directly oriented to the reaction space adjacent to the power supply electrode 110, whereby the gas passed the orifices 145 are not mixed enough. This causes irregular pressure distribution in the mixture space and fails supplying uniform pressure gas along the longitudinal direction of the power supply electrode 110, resulting in unstable plasma generation.